Why do humans need energy?

Why do humans need energy?

Carbohydrates, fats, proteins. We come across these terms on a daily basis, whether they’re mentioned in a health article, discussed on a podcast or radio show about dieting, or listed on the back of food packaging. And there’s a good reason why they’re so deeply enmeshed in our lives – they’re essential nutrients that our bodies use for energy.1

We get carbohydrates, fats and proteins via the food we consume. During digestion, these organic compounds are broken down to produce energy by the process of hydrolysis,2 a chemical reaction involving another essential nutrient – water.3

But why do humans need energy? What is that energy used for? Every human body has a Total Energy Expenditure (TEE), and in this article we look at the three major contributors to TEE, and what role sleep plays on energy supply.

Maintaining vital functions

There are many complex chemical processes taking place within the body that ensure the body stays alive and well. These processes, as a whole, are referred to as metabolism. Metabolism tends to have three main purposes: the breakdown of food into chemical energy to fuel cellular processes; the conversion of food into building blocks such as fatty acids, amino acids or sugars that the body uses for growth and repair; and the elimination of waste by-products.4

Metabolism requires a large amount of energy, and takes place all the time. This means that the body at rest is still very much at work – maintaining vital functions such as breathing, pumping blood, and ensuring organs like the heart, lungs, intestine and so on continue to operate as usual.

The minimum level of energy required to maintain the body’s vital functions is known as the Basal Metabolic Rate (BMR).5 And BMR just so happens to be the largest contributor to the body’s Total Energy Expenditure (TEE),6 accounting for roughly 60 to 75% of total daily energy expenditure for those living a sedentary lifestyle.7

Metabolising Food

Another contributor to TEE is the Thermic Effect of Food (TEF), which refers to the increase in the body’s metabolic rate after consuming a meal. Essentially, the body has energy requirements for digesting, absorbing and metabolising meals.8 Studies suggest TEF contributes to about 10% of our daily energy expenditure.9

Physical activity

The third major source of energy expenditure in the body is the Thermic Effect of Activity or physical activity.10 Depending on the individual and the lifestyle they lead, this may account for between 15 to 30% of total daily energy expenditure.11

Physical activity or activity-induced energy expenditure is split into two components: Exercise-related Activity Thermogenesis (EAT), and Non-Exercise-related Activity Thermogenesis (NEAT).12 The former refers to exercise done deliberately on a daily or weekly basis to improve one’s health and fitness, such as going to the gym or playing sports. The latter refers to physical activity that, as the name suggests, is not related to exercise, such as fidgeting, walking, climbing stairs, talking and other common activities of daily living.13

Sleep and energy expenditure

BMR, TEE and TEF all point to why humans need energy. There also happen to be plenty of factors which can influence energy expenditure, one of which is sleep.

When you sleep, your body is at rest. A study suggests that during this rest time, you burn approximately 40 to 55 calories per hour.14 This figure will of course vary from person to person depending on their BMR – which in turn is influenced by a number of factors such as age, diet, climate or race.15

Interestingly, studies also show that sleep helps to conserve energy in humans, and that sleep deprivation can result in increased energy expenditure.16 One study found that insufficient sleep actually led to an increase in weight gain, and this was because while energy expenditure increased by 5%, energy intake increased significantly in the night to be in excess of what the body needed to maintain energy balance.17 There is mounting clinical evidence that sleep, or lack of it, can influence body weight and contribute to obesity.18

These studies all confirm the importance of sleep for energy balance and good health.19 Sleep is vital to cognitive functioning, mental health, mood, and cardiovascular, cerebrovascular and metabolic health. It’s important to know how to sleep well.

If you find you are waking up feeling tired, and would like to feel more energised each morning, then consider trying B・SYNC ON – the wake up supplement that contains natural ingredients designed to help you wake up with ease.



  1. https://www.sciencedirect.com/science/article/pii/S221345301500004X
  2. https://www.sciencedirect.com/topics/physics-and-astronomy/hydrolysis
  3. https://www.nature.com/articles/ejcn2009111
  4. https://link.springer.com/referenceworkentry/10.1007/978-1-4419-1005-9_472
  5. https://link.springer.com/referenceworkentry/10.1007/978-1-4419-1005-9_377
  6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4278349/
  7. https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/basal-metabolic-rate
  8. https://pubmed.ncbi.nlm.nih.gov/8561055/
  9. https://www.tandfonline.com/doi/abs/10.1080/07315724.2018.1552544?journalCode=uacn20
  10. https://pubmed.ncbi.nlm.nih.gov/2691813/
  11. https://www.researchgate.net/figure/Components-of-total-daily-energy-expenditure-TDEEBMRbasal-metabolic-rate_fig1_260397860
  12. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6058072/
  13. https://www.cambridge.org/core/journals/proceedings-of-the-nutrition-society/article/nonexercise-activity-thermogenesis/30B928A57E8A92BB87A89FA006DB5ACD
  14. https://www.health.harvard.edu/staying-healthy/burning-calories-without-exercise
  15. https://jamanetwork.com/journals/jama/article-abstract/1156611
  16. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3039272/
  17. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3619301/
  18. https://jcsm.aasm.org/doi/10.5664/jcsm.2348
  19. https://jcsm.aasm.org/doi/10.5664/jcsm.9476